Debugging: provide access to private (non-exported) entities.#12367
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cfallin merged 3 commits intobytecodealliance:mainfrom Jan 21, 2026
Merged
Debugging: provide access to private (non-exported) entities.#12367cfallin merged 3 commits intobytecodealliance:mainfrom
cfallin merged 3 commits intobytecodealliance:mainfrom
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A debugger will need to access all entities (globals, tables, memories), even those that are not exported, in order to provide a full debugging experience: for example, a developer who has a debugger attached to a Wasm component will expect to be able to see data in its memory. Historically we have been very careful in Wasmtime to provide access to Wasm instances' entities only as the Wasm type system allows -- that is, only if they are exported. However, debugging is privileged -- in the same way that a native host debugger has `ptrace` and can view everything about the debuggee, we need to provide APIs for seeing through the encapsulation boundary. To ensure that this "violation of encapsulation" is scoped only to the extent needed for the legitimate need (debugging), this API is dynamically available only when `guest_debug` is configured true for a given engine. Otherwise, the accessor returns `None`. I opted not to provide a full introspection API that enumerates all of the entities as the debugger should already have access to the debuggee module and be able to enumerate the entities. Thus, the API only provides a host-API handle when asking for an entity by index in a given instance's index space.
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Reworked now -- a bit more verbose API but seems more in line with what is there already. Thanks! |
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FWIW we more-or-less consider wasmtime-environ to be a private crate for now. It's "more public" than everything else we have that's not actually public given its history, but we haven't pulled the trigger on making it actually official or anything like that. I think it would need a lot of API cleanups to have the same quality as wasmtime-the-crate.
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A debugger will need to access all entities (globals, tables, memories), even those that are not exported, in order to provide a full debugging experience: for example, a developer who has a debugger attached to a Wasm component will expect to be able to see data in its memory.
Historically we have been very careful in Wasmtime to provide access to Wasm instances' entities only as the Wasm type system allows -- that is, only if they are exported. However, debugging is privileged -- in the same way that a native host debugger has
ptraceand can view everything about the debuggee, we need to provide APIs for seeing through the encapsulation boundary.To ensure that this "violation of encapsulation" is scoped only to the extent needed for the legitimate need (debugging), this API is dynamically available only when
guest_debugis configured true for a given engine. Otherwise, the accessor returnsNone.I opted not to provide a full introspection API that enumerates all of the entities as the debugger should already have access to the debuggee module and be able to enumerate the entities. Thus, the API only provides a host-API handle when asking for an entity by index in a given instance's index space.